Pesticide resistance in coffee berry borers

The coffee berry borer, or broca (Hypothenemus hampei) is the most serious insect pest of coffee. Originally native to Africa, it has been unintentionally introduced to just about every coffee-producing nation in the world. Female beetles lay 30-50 eggs inside a coffee cherry, which hatch and develop inside. Thus, they damage the cherry and cause defects or the cherry drops off the tree and causes a loss. Economic impact can be substantial.

Nearly the entire life cycle of this very tiny beetle takes place inside the coffee ripening coffee cherry. For that reason, pesticides can be largely ineffective against it. Nonetheless, the neurotoxic organochlorine insecticide endosulfan is widely used in coffee farms to try to fight the borers. Not only is this not very effective, it is bad for the environment, and the life history of these beetles enables them to rapidly develop resistance to endosulfan.

Many cases of poisoning of coffee workers by endosulfan in Colombia resulted in a ban in that country in 2001. Endosulfan, to be even marginally effective, requires rather intensive spraying because of the relatively low probability of making contact with borer beetles that are actually outside of a coffee cherry and the high concentration needed for vapor to cause mortality of any beetles that have penetrated the skin of a coffee cherry.

Even when pesticides are banned in developed nations, they may continue to be used for many years in developing countries, such as coffee growing nations. Endosulfan is toxic to insects and animals (including humans) and can persist in the environment. Pesticides are frequently applied in these countries without proper safety precautions. At a recent coffee conference, Ernest Carmen of Costa Rica’s Cafe Cristina said that endosulfan is regulated and considered toxic in Costa Rica, but that it is freely available and indiscriminately applied, even though it is not that effective against broca.

What makes coffee berry borers so able to develop resistance to endosulfan?Coffee berry borers have an interesting life history that enables them to readily develop pesticide resistance. Most borers are females (13 to each male). All males are flightless, and mate with their sisters because they never leave the cherry in which they are born. This results in genetic inbreeding. When the mutation for endosulfan resistance pops up, it can rapidly spread through a population because of this inbreeding [1,2]. This has already occurred on the island of New Caledonia [3], and would be devastating if (or when) it happens in a mainland coffee producing region.

Alternate solution: promote shade coffee and habitat preservation to control pests!This study found ground-foraging ants are more common and eat more coffee berry borers in fallen coffee cherries in shade coffee than on sun coffee farms. This one found that coffee farms that had little shade also had fewer beetle species — except they had a much higher abundance of coffee berry borers. And this study showed that at coffee farms which were close to natural habitat patches, migratory birds preyed upon coffee berry borers, enough to bestow a healthy economic benefit to farmers.

New biocontrol methods, especially the role of natural predators associated with shade, is an area that is and will continue to draw more research attention.